FAQ - Total usable capacity in VMFS6

Products

• VMware vSphere ESXi

Issue/Introduction

After accounting for overhead, what's the total usable capacity of a VMFS6 datastore when its presented to a cluster of ESXi hosts.

Environment

VMFS6
ESXi

Cause

A very small percentage of the raw LUN capacity is used for overhead hence, the resulting VMFS6 datastore will not be an exact match in size of the raw LUN

Resolution

Overhead is very minimal and usually between the range 0.5–2%.
It usually depends on the size of the LUN that the VMFS6 datastore is created from.
For smaller LUNs its usually between 1.5–2%
For larger LUNs (5TB–64TB) its between 0.5–1.5%
Overhead includes: metadata, journaling, heartbeat regions, lock management, etc.

You may verify by running the following commands:

1. This will give you the size of the raw LUN
   esxcfg-scsidevs -c
2. This will give you the size of the VMFS datastore
   esxcli storage filesystem list

Adding it to a cluster of hosts will consume space within the VMFS datastore and its almost negligible, in MBs regardless of the LUN size.